Balloon angioplasty has been very effective in treating stenosis, i.e., to open blocked vessels and restore normal levels of blood flow. However, although once a blocked vessel is opened, the treated vessel has a tendency to restenose, i.e., reclose, shortly after the procedure. Thus, patients have to repeatedly be treated with angioplasty or surgery.
Implantable stent prosthesis or stents are used to reduce restenosis after balloon angioplasty or other procedures using catheters. A stent in the form of a wire mesh tube props open an artery that has recently been cleared using angioplasty. The stent is collapsed to a small diameter, placed over an angioplasty balloon catheter and moved into the area of the blockage. When the balloon is inflated, the stent expands, locks in place and forms a scaffold to hold the artery open. Usually, the stent stays in the artery permanently, holds it open, improves blood flow to the heart muscle and relieves symptoms. The stent procedure is fairly common, and various types of stents have been developed and actually used.
However, the metal surfaces of stents currently in use may trigger restenosis. To prevent the stented arteries from reclosing, patients who receive stents must take one or more anticoagulating drugs, such as heparin, aspirin, coumadin, dextran, and/or persantine even though systemic application of anticoagulants has been known to cause bleeding complications.
To reduce the likelihood of restenosis caused by the metal surface of such stents, stents covered with polymers and a drug have been offered. However, those covered stents are still not completely satisfactory. Therefore, there is a need for additional devices or methods to reduce the necessity for systemic application of anticoagulants and alleviate restenosis.
Further, for certain diseases which are localized to a particular part of body, the systemic administration of a biologically active material for the treatment of these diseases may not be preferred because of the inefficiencies associated with the indirect delivery of the biologically active material to the afflicted area. Therefore, there is a need for a device or method to deliver the biologically active material directly to a particular part of the body.